package net.abhinavsarkar.algorist.sort;

import java.lang.reflect.Array;
import java.util.Arrays;
import net.abhinavsarkar.algorist.Sorter;

public class MergeSorter<T> implements Sorter<T>
{
    @Override
    public T[] sort(T[] input, Comparator<T> comparator)
    {
        if (input.length == 0) {
            return input;
        }
        return this.sort(input, 0, input.length, comparator);
    }

    private T[] sort(T[] input, int start, int end, Comparator<T> comparator)
    {
        if (start == end - 1) {
            T[] output = mkArray(input, 1);
            output[0] = input[start];
            return output;
        }

        int half = start + (end - start)/2;
        T[] left = this.sort(input, start, half, comparator);
        T[] right = this.sort(input, half, end, comparator);
        return this.merge(left, right, comparator);
    }

    private T[] merge(T[] left, T[] right, Comparator<T> comparator)
    {
        T[] output = mkArray(left, left.length + right.length);
        int i, j, k;
        i = j = k = 0;
        while (i < left.length || j < right.length) {
            if (i >= left.length) {
                System.arraycopy(right, j, output, j + left.length, right.length - j);
                break;
            }
            if (j >= right.length) {
                System.arraycopy(left, i, output, i + right.length, left.length - i);
                break;
            }
            output[k++] = comparator.compare(left[i], right[j]) <= 0 ? left[i++] : right[j++];
        }

        return output;
    }

    @SuppressWarnings("unchecked")
    private T[] mkArray(T[] input, int length)
    {
        return (T[]) Array.newInstance(input.getClass().getComponentType(), length);
    }

    public static void main(String[] args)
    {
        Sorter<String> sorter = new MergeSorter<>();
        String[] sorted =
                sorter.sort(new String[]{"abhinav", "sarkar", "barista", "jordan", "data"},
                        (s, anotherString) -> anotherString.compareTo(s));
        System.out.println(Arrays.toString(sorted));
    }
}